Not an expert, I use a whetstone with quite a bit of water and aim to "cut the water": the edge pushes water along the stone if it's properly (or at least usably) angled. Once I have the angle in, I adjust my grip, or support the backside of the knife with my thumb, or whatever else lets me keep that angle consistent.

Bear in mind the angle might "change" on you as you sharpen a curved blade - or that's my shitty technique. I try to keep thinking about "the normal" or what's perpendicular to the edge where it's touching the stone.

Also, tip courtesy of Ethan Chlebowski on Youtube. You can use a permanent marker and color in the edge of the blade. Dye left on the edge means you're off and its distance from the... uh... edge of the edge will tell you if you're too shallow or too steep.

I can usually get my knives sharp enough that I haven't bothered with the marker trick. It's clever, though.